Automatic retractable ground electrical connector

ABSTRACT

A three prong electrical connector or plug having a spring biased grounding prong of sufficient strength to retain the ground prong extended for insertion into a three way electrical outlet and to allow the ground prong to retract when the plug is inserted into a two way electrical outlet. For plugs having a relatively short longitudinal dimension, the grounding prong is made of telescopic sections. A small conductive strip is provided to be secured to the face plate screw of a two way electrical outlet so that the ground prong is grounded even in the retracted position.

ite States McDaniel Jan. 15, 1974 AUTOMATIC RETRACTABLE GROUNDELECTRICAL CONNECTOR [76] Inventor: Johnny B. McDaniel, 4210 Stanby Ct.,Alexandria, Va. 22312 [22] Filed: Sept. 20, 1972 [21] App]. No.: 290,506

[52] US. Cl. 339/14 P, 339/31 R [51] Int. Cl ..1H01r 3/06 [58] Field ofSearch 339/14 R, 14 P, 14 RP, 339/31 R, 31 B, 31 L, 31 M, 31 T, 32 R, 32M, 33

[56] References Cited UNITED STATES PATENTS 3,739,317 6/1973 Wise 339/14R 3,308,415 3/1967 Cramer et a1. 339/14 R 3,685,000 8/1972 Robbins...339/14 P 3,531,757 9/1970 Alden 339/14 P FOREIGN PATENTS OR APPLICATIONS902,775 8/1962 Great Britain 339/31 R Primary Examiner-Marvin A.Champion Assistant Examiner-Robert A. I-lafer AtI0rneyMorris Fidelman etal.

[5 7] ABSTRACT A three prong electrical connector or plug having aspring biased grounding prong of sufficient strength to retain theground prong extended for insertion into a three way electrical outletand to allow the ground prong to retract when the plug is inserted intoa two way electrical outlet. For plugs having a relatively shortlongitudinal dimension, the grounding prong is made of telescopicsections. A small conductive strip is provided to be secured to the faceplate screw of a two way electrical outlet so that the ground prong isgrounded even in the retracted position.

13 Claims, 7 Drawing Figures WENTEWM 15 m4 44 I Iii FIG/6 AUTOMATICRETRACTABLE GROUND ELECTRICAL CONNECTOR FIELD OF THE INVENTION Thisinvention relates generally to a three prong electrical connector andmore specifically to a three prong electrical connector having anautomatic retractable ground plug.

DESCRIPTION OF THE PRIOR ART The National Safety Council recordsannually hundreds of electrical shock incidents and many fatalhome/industrial electrocution accidents caused in whole or part bynon-grounded electrical power tools and appliances. Additionally, asevere shock hazard exists when power tools and appliances are in useduring an electrical storm; where an over-voltage or power lineshort-circuit may inadvertently charge the frame of the appliance with apotential lethal voltage.

Most modern appliances now feature an internal ground for the motor tothe frame and the convenience outlet by the use of a third groundingcable contained in the power cord set. In older homes, offices orindustrial facilities where the convenience outlets lack a proper groundopening and lug, the use of an adapter plug socket connector provideselectrical poer to the appliance but may not afford any degree of groundprotection. Some of the adapter wire plugs feature a green coded groundwith a connector lug that may be connected beneath the central threadedscrew that attaches the receptacle over plate to the convenience outlet.The National Safety Council points out that most people neglect to makethe required connection even if provided because of the followingreasons: lack of an available screwdriven in a hurry;" didnt understandwhat the wire was for; etc., etc.

All adapter plug-sockets exhibit a common troublesome problem for theuser, that being, when connected between the appliance connector and theconvenience outlet, the resulting combination tends to sag and pull awayfrom the convenience outlet due to the weight or movement of theappliance cord set. This often results in an electrical OPEN as the malesabre pulls free of the connector with the appliance losing power orarcing and pitting occurring within the convenience outlet terminals.These and other difficulties may be experienced with prior art devicesbut are now made obsolete by the novel design feature of this presentinvention.

The prior art is replete with examples of attempts to provide a threeprong plug with a feature to allow the grounding plug to be removed fortwo wire outlets.

. Some have even provided locking mechanisms to manually move the pronginto the body of the plug and lock it in either the retracted or theextended position. However, none of the plugs of the prior art provide ameans to ground the three wire plug to a two wire terminal. Also withoutsuch additional means, the three wire plugs become essentially a twowire plug that is ungrounded, therefore the use of the appliance isunsafe.

SUMMARY OF THE INVENTION The present invention is a three wire plughaving a spring loaded, automatically retractable ground. The groundingprong mechanically and electrically contacts a metal housing and slidestherein. 'A positive spring action provides the required tension toallow the grounding prong'to be normally inserted into a three apertureoutlet, and allows the prong to retract within the body for use in theolder two aperture outlets. A piece of conductive metal is provided toestablish a connection between the cover plate screw which is groundedand the face of the outlets so that the retracted electrical prong isgrounded. For the low profile flatback or short plugs, the groundingprong may be composed of telescopic sections.

OBJECTS OF THE INVENTION An object of the present invention is toprovide a foolproof electrical cord-set connector that automaticallygrounds, retracts and adapts to any convenient outlet without thetroublesome burden of using a separate adapter plug-set and/or pigtailedground wire extensions.

Another object of the invention is to provide an automaticallyretractable ground that is simple in construction, use and manufacturingtechniques.

A further object of the invention is to provide an electrical groundprong which is redundantly connected to the ground wire.

Still another object is to provide an automatically retractable groundfor the low profile flat-back or narrow plugs.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective sectionalbreak-away side view of the male connector plug;

FIG. 2 is a sectional break away view of an alternate embodiment of thegrounding prong and casing;

FIG. 3 is a cross-sectional view of a third embodiment of the groundingprong and casing;

FIG. 4 is a side view of the conductive strip for use in older two-holereceptacles;

FIG. 5 is a front view of the use of the conductive strip with the oldertwo-hole receptacles;

FIG. 6 is a perspective sectional break-away side view of a telescopicretractable grounding prong in a low profile flatback male connectorplug; and

FIG. 7 is a side view of a locking pin.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1, which illustrates apreferred embodiment of the present automatic retractable groundelectrical connector, shows a plug 10 and a three conductor electricalcord 12 attached thereto. Two of the electrical connectors of the cord12 are electrically and mechanically connected to two male prongs l6 and17. In the perspective cut away view, electrical connector 14 is shownconnected to male prong 16 at point 18. The electrical cord, as well asthe two male prongs and the retractable ground prong, are all housed ina body 20 made of suitable insulating material. The forming of the body20 with the three male prongs electrically connected to the threeelectrical conductors of the cord 12 is well known in the art. Forexample, this may be done with mold injection machines or any similarlyknown device of the prior art.

The ground conductor 22 of electrical cord 12 is attached to groundprong casing 24 at the end thereof by soldering, for example. Insidecasing 24 is the grounding prong 26. The grounding prong slides alongthe interior of casing 24 and makes mechanical and electrical contactthereto. The resilient spring 28 is attached to the rear of casing 24and is electrically connected to ground conductor 22. The other end ofspring 28 applies a force against the ground prong 26. Spring 28 may beattached to the enclosed end of prong 26. Thus a redundant electricalconnection of the electrical conductor 22 to ground prong 26 is madethrough the easing 24 and the spring 28. Thus, if either one of thegroundpaths should be broken, the other one will provide electricalcontinuity for an efficient and safe ground.

The grounding prong 26 of FIG. 1 is shown to be completely cylindricalwith a tapered tip. Ground prong 26 in the fully extended positionextends past the other prongs 16 and 17 as required by the NationalElectrical Code. The length and strength of spring 28 is such that thegrounding prong 26 will remain extended and will insert into aconventional three hole or apertured wall outlet. Upon the insertion ofplug into the older two hole outlet, the grounding prong 26 will retractagainst the force of spring 28 back into the casing 24. The length ofspring 28 is such that the rear end of grounding prong 26 at which thespring 28 is connected, will never leave the casing 24 and therefore theinsulated body 20. The simplicity of the design of FIG. 1 and theminimum number of parts guarantees the versatility and high mechanicalreliability of the retractable grounding plug. Also the use of minimumparts extends the useful life of the present plug. An aperture 27 isprovided in grounding prong 26 to receive a locking pin 94. If spring 28should break, grounding prong 26 can be locked in the fully extendedposition inserting tapered end 96 of locking pins 94 in aperture 27. Thelocking pin 94 is illustrated in FIG. 7, having a head portion 98 and atapered end 96. The pin remains secured in the aperture 27 due to thetapered shape of end 96. The locking plug is made of nyon or plastic. Asdescribed above, the present invention insures grounding through thecasing if the spring should break. If the shape of the connectors bodydoes not have a major recess for the grounding prong as shown in FIG. 1,the head portion 98 of the locking pin 94 could be eliminated.

An alternate embodiment of the grounding plug and its casing is shown inFIG. 2. The casing 30 has two longitudinal channels 32 and 34 diagonallyacross from each other. Within these channels slide protrusions 36 and38 of electrical ground prong 40. The ground prong 40 is prevented fromleaving the casing 30 by a from shoulder 42. Simple manufacturingtechniques are known for extruding the casing 30 with the two channels32 and 34 therein. Without the use of the shoulder 42, the ends of thechannels may be crimped so as to prevent the protrusions 36 and 38 fromleaving the housing. As in the previous embodiment of FIG. 1, a spring43 is provided which produces a positive resilient force against thegrounding prong 40 for its use as described above. Also the springprovides a redundant electrical ground connection. The channels 32 and34 provide a guide for protrusions 36 and 38 and prevent rotationalmovement of the grounding prong 40. As in the previous embodiment, anaperture 41 is provided in prong 40 to receive locking pin 94.

Another alternate embodiment of the ground prong and casing is shown inFIG. 3. Here the casing 44 is shown as having a from shoulder 46extending radially therefrom. The grounding prong 48 has a rearretention shoulder 50 which slides along and makes electrical andmechanical contact with the casing 44. The retention collar 50terminates or abuts in the fully extended position at the front shoulder46 of casing 44. As in the other embodiments, a spring 52 exertspositive mechanical force against the rear retention shoulder 50 andprovides redundant electrical contact.

As mentioned above, there is always a chance that the spring 52 mayweaken from extended use before the rest of the plug, in which case, theelectrical continuity between the ground electrical connector and thegrounding prong is maintained through the casings. Thus a means must beprovided to allow the prongs to be mechanically manipulated to stay inthe extended position or be allowed to retract. FIG. 3 shows a hole oraperture 54 in the side of casing 44. If the spring 52 should break, theprong 48 could be mechanically pulled forward and held in that positionwhile the nylon or plastic locking pin 94 could be inserted through slot54 which would be located behind the rear retention shoulder 50 when theprong 48 is fully extended. Thus the shoulder 46 of casing 44 and therear retention shoulder 50 of ground prong 48 would be abutting and heldthere by the locking pin 94 inserted into aperture 54.

The problem still remains of maintaining ground continuity between theplug 10 and the older two way wall outlet. To provide this continuity,the present invention includes an electrical conductor 56 as shown inFIG. 4. The conductor is shown as having a center section 58 and tworaised parallel sections 60 and 62. Center section 58 has a hole 59 forreceiving an electrical outlet cover plate screw. The two raisedparallel sections 60 and 62 have holes 61 and 63, respectively, forreceiving the ends of the automatically retractable grounding prong ofthe present invention. The holes 61 and 63 are smaller than thegrounding prongs so as to assure maximum continuous electrical contact.Preferably, the diameter of holes 61 and 63 should be approximately 2/3of the diameter of the grounding prong. Sections 58, 60 and 62 may allbe in the same plane, depending on the contour of the electrical outletand its face plate.

A conventional two socket electrical outlet is shown in FIG. 5 as havinga face plate 64 retained to the outlet by screw 66. Theoutlet has twosockets 68 and 70 having female receiving apertures 72, 74 and 76 and78, respectively. The electrical conductor 56 is retained by screw 66through a hole or aperture 59. The two parallel raised sections 60 and62 of electrical conductor 56 rest on the face of outlet 68 and 70respectively. These two surfaces lie in the position at which the groundor third aperture would be on the newer conventional three aperturedwall outlet or sockets. Since the electrical box itself is normallygrounded and screw 66 is connected to the box, an electrical circuit iscreated to the ground through the screw and the electrical-conductor 56.Thus when an electrical plug or connector of the present invention, asillustrated in FIGS. 1-3, is applied to the older, two aperturedelectrical outlets, the grounding prong is retracted partially into itscasing and maintains electrical contact to ground through the electricalconductor strip 56, screw 66 and the electrical outlet box. Thus even inthe retracted position, the present invention provides an electricalcircuit to ground and consequently the safe use of the appliance to theconsumer.

Unlike the solution of grounding adapters of the prior art having anelectrical wire which must be applied to the center screw each time aportable appliance or tool is used, the present invention provides asimple conductive strip which may be applied and left on all electricaloutlets. Thus the consumer would not be faced with the bother ofelectrically connecting ground every time. As indicated above, it isthis inconvenience which is the main cause of not grounding equipmentwhich requires a ground and thus increases the liklihood ofelectrocution. Thus the present invention has provided a combination ofa fully automatic, retractable ground and a conductive strip which maybe permanently installed to all electrical outlets such that theretractable electrical connector of the present invention will provideand maintain ground for the portable equipment being used.

In many present day applications, the electrical plug or connector doesnot allow for the use of an extremely long body as shown in FIG. 1.Thus, for example, in electrical dryers and air conditioners, a flat orshort plug is used as shown in FIG. 6. The three wire electricalconductor 82 is shown extending from the side of the low profile, shortflat-back body 80. Besides the two normal male electrical prongs 84 and85, there is the automatically retractable grounding prong of thepresent invention. As before, the grounding wire is shown electricallyconnected to casing 86 and spring 88. Because of the size of the body80, the grounding prong of the present invention must be made in atleast two telescopic sections 90 and 92. The ends of the telescopicsections are slightly enlarged so that the ends of section 90 areretained in section 92 and the end of section 92 is retained in casing86. This allows for the extending and retracting of the sections toperform as described above. The resilient spring is connected to thesmallest diameter telescopic section 90.

Upon insertion of the plug 80 into a normal three socket electricaloutlet, the telescopic sections 90 and 92 are inserted into thegrounding aperture. Upon application of the plug 80 into a conventionaltwo aperture outlet having the conductive grounding strip 56 attachedthereto, telescopic section 90 retracts within telescopic section 92,which also retracts partially within the casing 86 while maintainingelectrical continuity through the conductive strip 56. Thus theautomatically retractable grounding prong as illustrated in FIGS. 1-3 isadapted for use in the shorter or flat-back plug of FIG. 6. As in theother embodiments, the grounding prong may have an aperture to receivethe locking pin 94.

It should be noted that all of the embodiments of the present inventionshow the grounding prong snugly fitting within its casing. This featureprevents foreign matter, such as dirt or grease, from interfering withthe motion of the ground prong as would be the case in many prior artdevices. Thus the present invention provides an automaticallyretractable electrical connector with redundant ground connection whichprovides a guaranteed ground to a two or three aperture electricaloutlet using the minimum number of moving mechanical parts and thereforeproviding a cheap and long-lasting electrical connector.

Although the invention has been described and illustrated in detail, itis to be clearly understood that the same is by way of illustration andexample only and is not to be taken by way of limitation, the spirit andscope of this invention being limited only by the terms of the appendedclaims.

What is claimed:

1. A plug in combination with a three conductor electrical cordcomprising:

a body;

two prongs securely embedded in said body and electrically connected totwo of said conductors;

a conductive general cylindrical casing completely embedded in saidbody, electrically connected to the third conductor which is to begrounded, and having a longitudinal channel extending substantially thelength of said casing;

a grounding prong having a protrusion extending radially from saidgrounding prong and adapted to slide within said channel, therebypreventing rotation of said grounding prong; a spring biasing means insaid casing connected to one end of said ground prong and being ofsufficient resilience to independently automatically maintain saidgrounding prong extended when said plug inserts into a three hole socketand automatically allowing said grounding prong to retract within saidcasing when said plug inserts into a two hole socket.

2. A plug as in claim 1 wherein said biasing means comprises a springmechanically and electrically secured to the interior of said casing andthe interior of said grounding prong so as to provide redundantelectrical contact between said third conductor and said groundingprong.

3. A plug in combination with a three conductor electrical cordcomprising:

a body;

two prongs securely embedded in said body and electrically connected totwo of said conductors;

a conductive general cylindrical casing completely embedded in saidbody, electrically connected to the third conductor which is to begrounded, and having one end exposed;

a grounding prong having a radial aperture and slidably engaging saidcasing and making electrical contact thereto;

a tapered locking pin adapted to be inserted and retained in said radialaperture to lock said grounding prong when extended; and

spring biasing means electrically and mechanically connecting theinterior of said casing and said grounding prong so as to provideredundant electrical contact between said third conductor and saidgrounding prong and automatically maintaining said grounding prongextended when said plug inserts into a three hole socket andautomatically allowing said grounding prong to retract within saidcasing when said plug inserts into a two hole socket said ground prongbeing freely slidable in said casing when said locking pin is not inuse, said spring means exerting sufficient force to keep said groundprong extended upon entry into a three-hole electrical receptable.

4. A plug as in claim 3 wherein said casing and said body includesuperimposed radial apertures which are juxtapositioned to saidgrounding prongs radial aperture when said grounding prong is fullyextended.

5. A plug as in claim 3 wherein said grounding prong comprises aplurality of cylindrical members of different diameters interconnectedtelescopically.

6. A plug as in claim 5 wherein the spring is electrically andmechanically connected to said cylindrical member of the smallestdiameter.

7. An automatically retractable ground electrical connector system forconnecting and grounding a three conductor cord to either a two or threefemale electrical receptacle, said system comprising:

a body of insulated material attached to said cord;

two fixed prongs secured in said body and electrically connected to twoof said three conductors;

generally cylindrical conductive casing secured within said body andelectrically connected to the remaining ground conductor of said threeconductors;

a third prong slidably received in one end of said conductive casing andelectrically connected to said conductive casing;

a spring secured mechanically and electrically to the other end of saidconductive casing and to said third prong urging said third prong toextend from said body;

a generally rectangular conductive element, with an aperture which isadapted to receive a screw of the receptacles face plate, adapted toextend over part of the receptacle and abut said third prong when saidprong is inserted in said receptacle thereby grounding said third prong;

said spring having sufficient resiliency to maintain said third prongextended when said prong is inserted in the ground aperture of a femaleelectrical receptacle, said third prong being automatically retractedinto said body when said third contact engages and remains in contact,by the urging of said spring, with said rectangular conductive element.

8. An automatically retractable ground electrical connector as in claim7 wherein said casing includes a longitudinal channel extendingsubstantially the length of said casing and said third prong includes aprotrusion extending radially from said third prong and adapted to movewithin said channel, thereby preventing rotation of said third prong.

9. An automatically retractable ground electrical connector as in claim7 wherein said third prong comprises a plurality of cylindrical membersof different diameters inter-connected telescopically.

10. An automatically retractable ground electrical connector as in claim9 wherein said spring is electrically and mechanically connected to saidcylindrical member of the smallest diameter.

11. An automatically retractable ground electrical connector as in claim7 wherein said rectangular conductive element includes a center portionand two end portions vertically displaced from said center portion.

12. An automatically retractable ground electrical connector as in claim7 wherein said rectangular conductive element includes at least a secondaperture adapted to receive said third prong.

13. An automatically retractable ground electrical connector as in claim12 wherein said second apertures diameter is less than the diameter ofsaid third prong.

1. A plug in combination with a three conductor electrical cordcomprising: a body; two prongs securely embedded in said body andelectrically connected to two of said conductors; a conductive generalcylindrical casing completely embedded in said body, electricallyconnected to the third conductor which is to be grounded, and having alongitudinal channel extending substantially the length of said casing;a grounding prong having a protrusion extending radially from saidgrounding prong and adapted to slide within said channel, therebypreventing rotation of said grounding prong; a spring biasing means insaid casing ''''connected to one end of said ground prong and being ofsufficient resilience to independently'''' automatically maintain saidgrounding prong extended when said plug inserts into a three hole socketand automatically allowing said grounding prong to retract within saidcasing when said plug inserts into a two hole socket.
 2. A plug as inclaim 1 wherein said biasing means comprises a spring mechanically andelectrically secured to the interior of said casing and the interior ofsaid grounding prong so as to provide redundant electrical contactbetween said third conductor and said grounding prong.
 3. A plug incombination with a three conductor electrical cord comprising: a body;two prongs securely embedded in said body and electrically connected totwo of said conductors; a conductive general cylindrical casingcompletely embedded in said body, electrically connected to the thirdconductor which is to be grounded, and having one end exposed; agrounding prong having a radial aperture and slidably engaging saidcasing and making electrIcal contact thereto; a tapered locking pinadapted to be inserted and retained in said radial aperture to lock saidgrounding prong when extended; and spring biasing means electrically andmechanically connecting the interior of said casing and said groundingprong so as to provide redundant electrical contact between said thirdconductor and said grounding prong and automatically maintaining saidgrounding prong extended when said plug inserts into a three hole socketand automatically allowing said grounding prong to retract within saidcasing when said plug inserts into a two hole socket said ground prongbeing freely slidable in said casing when said locking pin is not inuse, said spring means exerting sufficient force to keep said groundprong extended upon entry into a three-hole electrical receptable.
 4. Aplug as in claim 3 wherein said casing and said body includesuperimposed radial apertures which are juxtapositioned to saidgrounding prong''s radial aperture when said grounding prong is fullyextended.
 5. A plug as in claim 3 wherein said grounding prong comprisesa plurality of cylindrical members of different diameters interconnectedtelescopically.
 6. A plug as in claim 5 wherein the spring iselectrically and mechanically connected to said cylindrical member ofthe smallest diameter.
 7. An automatically retractable ground electricalconnector system for connecting and grounding a three conductor cord toeither a two or three female electrical receptacle, said systemcomprising: a body of insulated material attached to said cord; twofixed prongs secured in said body and electrically connected to two ofsaid three conductors; a generally cylindrical conductive casing securedwithin said body and electrically connected to the remaining groundconductor of said three conductors; a third prong slidably received inone end of said conductive casing and electrically connected to saidconductive casing; a spring secured mechanically and electrically to theother end of said conductive casing and to said third prong urging saidthird prong to extend from said body; a generally rectangular conductiveelement, with an aperture which is adapted to receive a screw of thereceptacle''s face plate, adapted to extend over part of the receptacleand abut said third prong when said prong is inserted in said receptaclethereby grounding said third prong; said spring having sufficientresiliency to maintain said third prong extended when said prong isinserted in the ground aperture of a female electrical receptacle, saidthird prong being automatically retracted into said body when said thirdcontact engages and remains in contact, by the urging of said spring,with said rectangular conductive element.
 8. An automaticallyretractable ground electrical connector as in claim 7 wherein saidcasing includes a longitudinal channel extending substantially thelength of said casing and said third prong includes a protrusionextending radially from said third prong and adapted to move within saidchannel, thereby preventing rotation of said third prong.
 9. Anautomatically retractable ground electrical connector as in claim 7wherein said third prong comprises a plurality of cylindrical members ofdifferent diameters inter-connected telescopically.
 10. An automaticallyretractable ground electrical connector as in claim 9 wherein saidspring is electrically and mechanically connected to said cylindricalmember of the smallest diameter.
 11. An automatically retractable groundelectrical connector as in claim 7 wherein said rectangular conductiveelement includes a center portion and two end portions verticallydisplaced from said center portion.
 12. An automatically retractableground electrical connector as in claim 7 wherein said rectangularconductive element includes at least a second aperture adapted toreceive said third prong.
 13. An automatically retractable groundelectrical connector as in claim 12 wherein said second aperture''sdiameter is less than the diameter of said third prong.